Programming molecular switches in water and ethanol via thermo-sensitive polymers for phase control in energetic crystals

Abstract

The practical application of energetic materials, particularly 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), is frequently impeded by phase transition challenges. In this study, we propose a novel strategy to enhance the stability of CL-20 by employing a thermo-sensitive polymer, poly(N-isopropylacrylamide) (PNIPAM), to modulate its phase transitions. Our approach involves the use of an in-situ polymerized polydopamine (PDA) shell as a platform for surface grafting through atom transfer radical polymerization, yielding a core-shell structured CL-20@PDA-PNIPAM. Through comprehensive characterization, the successful grafting of PNIPAM is confirmed, significantly enhanced the phase stability of CL-20. Notably, our core-shell structure exhibits a 13 °C increase in phase transition temperature compared to raw CL-20, thereby delaying the ε→α phase transition by over 80 min under combined thermal and solvent conditions. The enhanced stability is attributed to the hydrophobic nature of PNIPAM above its low critical solution temperature in water, which effectively shields the CL-20 crystal. These findings provide new insights into enhancing the stability and safety of energetic materials in complex environments, highlighting the potential of our molecular switch mechanism.

Keywords

• 2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20)
• Phase stability
• Polydopamine (PDA)
• Poly-N-Isopropylacrylamide (PNIPAM)
• Thermal and solvent effects